London, June 30 (AP): Police mounted increased patrols in a jittery London today as detectives conducted an intense hunt for a man seen running from an explosives-packed car in the heart of the city’s entertainment district.

Two Mercedes cars loaded with fuel, gas canisters and nails were found abandoned yesterday in what police believe was an attempt to kill scores or even hundreds of people.

Detectives said they were keeping an open mind about the perpetrators, but terrorism experts said the signs pointed to a cell linked or inspired by al Qaida.

Prime Minister Gordon Brown was briefed today on the investigation and the security threat by counterterrorism officers at Scotland Yard and later chaired a meeting of intelligence officials, police and senior officials in Cobra, the government’s emergency committee, his office said.

Police would not comment on a report by the US network ABC News saying police had a “crystal clear” picture of one suspect from CCTV footage.

Forensic experts were searching the two cars for clues. One was abandoned outside the Tiger Tiger nightclub on Haymarket, a busy street of shops, clubs, theatres and restaurants just metres from Trafalgar Square and Piccadilly Circus. The other had been towed after being parked illegally on nearby Cockspur Street and was discovered in an impound lot about 1.5 km away in Park Lane near Hyde Park.

Deputy assistant commissioner Peter Clarke, the Metropolitan Police anti-terrorism chief, said the two devices could have caused “significant injury or loss of life”.

“The discovery of what appears to be a second bomb is obviously troubling and reinforces the need for the public to be alert,” he said.

The plot — uncovered a week before the second anniversary of the July 7 suicide bombings that killed 52 commuters on the city’s transit system — rattled Londoners.

“London on the Edge” said the front-page headline in The Independent newspaper while the Daily Mail wondered: “Where’s the Next Bomb'”

Mayor Ken Livingstone urged Londoners to remain vigilant.

“The discovery of two potential car bombs in central London, with those responsible still at large, means we face a very real threat of terrorist attack at this moment in time,” he said.

Police said they were strengthening patrols in the city to reassure the public, with 350 officers on duty to police the annual Gay Pride parade through central London, not far from where the bomb-laden cars had been parked.

Terrorism experts said the improvised devices discovered yesterday were similar to ones used by homegrown terror cells — including the bombs used in the July 7 attacks — although the discovery of the second device suggested a coordinated and more sophisticated attack, possibly a terror cell with links to al Qaida in Pakistan.

Intelligence officials were examining a post to an Islamist website — hours before the cars were found — that suggested Britain would be attacked for awarding a knighthood to novelist Salman Rushdie and for intervening in Muslim countries.

The US-based SITE Intelligence Group, which monitors extremist websites, said a post on the al-Hesbah forum asked: “Is London craving explosions from al Qaida'” and added: “I say the good news, by Allah, London will be hit.”

SITE said the message had been posted to an unmoderated, public section of the forum, and its relationship, if any, to the car bombs could not be verified.